Polyvinyl chloride has been and is widely used not only in the fields of industries and household articles but also in the fields of medical treatment and welfare. Particularly, most of disposable medical devices are produced from polyvinyl chloride. Since, however, soft polyvinyl chloride contains a relatively large amount of plasticizers such as dioctyl phthalate (DOP), etc., the problem of elution of the plasticizer into blood or a medicinal solution is pointed out from the viewpoint of safety of medical devices.
On the other hand, from the viewpoint of infection prevention, steps are taken forward to dispose medical devices, and it is required by the law to dispose of used medical devices by incineration. It is said that polyvinyl chloride generates almost no toxic chlorine-containing substances such as dioxin since it is converted finally to carbon dioxide, water and hydrogen chloride when combusted at a temperature of approximately 850 to 900° C. with feeding sufficient oxygen. In reality, however, the problem of environmental pollution with dioxin or other toxic chlorine-containing substance frequently takes place for reasons that there are not sufficient incinerators that can withstand said high temperatures, that there are small-sized incinerators of which the incineration capacity is insufficient and that there are few plants for dioxin disposal.
Studies are recently being made for changing the material in the fields of medical devices, industries and a household devices from the soft vinyl chloride to other materials.
As a polyvinyl-chloride-free material for medical tubes, studies are made on polyethylene (PE), polypropylene (PP), an ethylene-vinyl acetate copolymer (EVAC), polyethyl methacrylate (PEMA), a styrene-butadiene block copolymer, a hydrogenation product of a styrene-isoprene copolymer (styrene-based thermoplastic elastomer), and the like.
For example, as a resin composition that gives a molded article excellent in flexibility and suitable for medical use, JP-A-4-158868 (Literature 1), JP-A-4-159344 (Literature 2) and JP-A-8-131537 (Literature 3) propose a resin composition (styrene-based thermoplastic elastomer) containing an olefin resin, a hydrogenation product of a styrene-butadiene block copolymer (styrene-based thermoplastic elastomer) and a hydrogenation product of a styrene-isoprene block copolymer.
Further, JP-A-9-103493 (Literature 4) and JP-A-123314 (Literature 5) disclose a multi-layered tube formed of a substrate layer and an adhesive layer in which the adhesive layer is made of a material that is not dimensionally stable at an autoclave sterilization temperature (121° C.) or higher and tends to flow under a connection pressure with other tube having a different diameter during autoclave sterilization at 121° C.
(1) In principle, however, a tube made of the above PE, EVAC or PEMA has flexibility but has a problem that the tube, when made of a single material, is liable to undergo kinking (which refers to a phenomenon that the tube bends or is twisted to come into the state where internal surfaces of the tube become stuck or adhered together).
(2) While the above styrene-based thermoplastic elastomer as a single material or a composition containing 60 mass % thereof or more has flexibility, they come to have sticking nature on the surface when sterilized with high-pressure steam (autoclave sterilization), so that they are not suitable for use as a material to form a surface that will contact blood. Further, they have a problem that the internal surface of the tube undergoes self-sticking (self-adhesion) when the tube is clamped with a forceps and the tube shows poor restoration capability when it was released from clamping after occlusion.
(3) Further, a tube made of the above PP as a single material or a composition containing at least 40 mass % thereof is too rigid and not flexible enough to prevent 1=4 kinking.
The resin composition described in the above Literatures 1 to 3 has characteristic features that it gives a molded article excellent in flexibility and it does not involve the generation of an toxic gas such as dioxin when the molded article is incinerated. However, {circle around (1)} when emphasis is placed on flexibility, a single-layered tube made of the above resin composition has a higher proportion of the styrene-based thermoplastic elastomer, and the tube suffers problems that are not negligible, that is, it has poor heat resistance problem that the cross section of the tube sterilized in an autoclave is deformed or one tube is fused with another or a problem that the tube has poor restoration capability when released from clamping with a forceps after occlusion with it. {circle around (2)} When emphasis is placed on heat resistance and restoration capability after occlusion, the proportion of the styrene-based thermoplastic elastomer comes to be smaller, and the tube becomes less flexible and is not at all satisfactory as a medical tube. It is therefore desired to improve the tube in these points.
In a multi-layered tube, hot melt bonding or solvent bonding is the most preferred in view of reliable connection. In the multi-layered tube described in Literature 4 or 5, the adhesive layer is made of a material that is not dimensionally stable at an autoclave sterilization temperature (121° C.) or higher and tends to flow under a connection pressure with other tube having a different diameter during autoclave sterilization at 121° C., and the tube is connected to the other tube by “press fitting” between these tubes. These tubes are therefore intimately connected by adherence, so that one tube easily comes off from the other under small force. Further, since tackiness is caused under heat by the autoclave sterilization, fitted portions may come apart one from the other during the sterilization or at a step prior thereto, and it is considered that such a material is not suitable for producing medical devices.
As performances required for medical tube that can be sterilized with high-pressure steam, preferably, the tube satisfies the following conditions:
That is, (a) the tube is to have proper flexibility without keeping on kinking or bending when bent, (b) the tube is to show no stickiness (tackiness) on the surface and is to be free from any change in form and dimensions when sterilized with high-pressure steam, and (c) the tube permits hot melt bonding or solvent bonding when connected to other tube having a different diameter or an injection-molded article.
As described above, it is an object of the present invention to provide a multi-layered tube which is excellent in transparency, flexibility, anti-kinking properties, restoration capability after occlusion and heat resistance and which elutes no plasticizer and generates no toxic gas when incinerated, and to provide a medical device comprising said multi-layered tube.